Optical scanner devices are well-known in the art and produce machine-readable image data signals that are representative of a scanned object, such as a photograph or a page of printed text. In a typical scanner application, the image data signals produced by an optical scanner may be used by a personal computer to reproduce an image of the scanned object on a suitable display device, such as a CRT or a printer.
A hand-held or portable scanner is an optical scanner which is designed to be moved by hand across the object or document being scanned. The hand-held scanner may be connected directly to a separate computer by a data cable. If so, the data signals produced by the hand-held scanner may be transferred to the separate computer "on the fly," i.e., as the image data are collected. Alternatively, the portable hand-scanner may include an on-board data storage system for storing the image data. The image data may then be downloaded to a separate computer after the scanning operation is complete by any convenient means, such as via a cable or an optical infrared data link.
Hand-held or portable optical scanners are well-known in the art and various components thereof are disclosed in U.S. Pat. No. 5,552,597 of McConica for "Hand-Held Scanner having Adjustable Light Path", U.S. Pat. No. 5,586,212 of McConica, et al., for "Optical Wave Guide for Hand-Held Scanner," U.S. Pat. No. 5,381,020 of Kochis, et al., for "Hand-Held Optical Scanner with Onboard Battery Recharging Assembly," and U.S. Pat. No. 5,306,908 of McConica, et al., for "Manually Operated Hand-Held Optical Scanner with Tactile Speed Control Assembly," all of which are hereby incorporated by reference for all that they disclose.
A typical hand-held optical scanner may include illumination and optical systems to accomplish scanning of the object. The illumination system illuminates a portion of the object (commonly referred to as a "scan region"), whereas the optical system collects light reflected by the illuminated scan region and focuses a small area of the illuminated scan region (commonly referred to as a "scan line") onto the surface of a photosensitive detector positioned within the scanner. Image data representative of the entire object then may be obtained by sweeping the scan line across the entire object, usually by moving the hand-held scanner with respect to the object. By way of example, the illumination system may include a light source (e.g., a fluorescent or incandescent lamp or an array of light emitting diodes (LEDs)). The optical system may include a lens and/or mirror assembly to direct and focus the image of the illuminated scan line onto the surface of the detector. The optical system may also comprise a reduction optics system for reducing the reflected light onto a very small detector.
The photosensitive detector used to detect the image light focused thereon by the optical system may be a contact image sensor, an array of photodetectors which act together to capture the image of a scan line. A typical individual photodetector changes electrical resistance as it is exposed to light. As the intensity of the light reflected from the image onto the photodetector changes, the electrical current passing through the photodetector varies. Thus a photodetector may be used to detect light and dark regions on an image.
The term "image light" as used herein refers to the light that is focused onto the surface of the detector array by the optical system. Depending on the type of scanner and the type of document, the image light may be reflected from the document or object being scanned or it may be transmitted through the object or document. The image light may be converted into digital signals in essentially three steps. First, each photodetector converts the light it receives into an electric charge. Second, the charges from the photodetectors are converted into analog voltages by an analog amplifier. Finally, the analog voltages are digitized by an analog-to-digital (A/D) converter. The digital data then may be processed and/or stored as desired.
A typical hand-held optical scanner may also include a position sensing system to keep track of the scanners position with respect to the object. A position sensing system may comprise several optical detectors, or navigators, which capture the image of several target locations on the object. The position sensing system allows a portable scanner to image an object or document which is larger and wider than the scanner. As the portable scanner is moved back and forth across the object to scan all areas of the object, the position sensing system keeps track of the position of the scanner. The various scanned strips may then be "stitched" together using the position information collected by the position sensing system.
One type of optical position sensor is a two dimensional array of optical detectors which generates image data representing a two-dimensional portion of the surface of the object. A processor analyzes the image data to identify the positions of distinct features located on the surface of the object relative to the optical sensor. As the scanner is moved relative to the object, the positions of these distinct features relative to the optical sensor move accordingly. The processor measures these position changes to determine the displacement and direction of movement of the scanning device relative to the surface of the object. The processor may also integrate the displacement to determine the velocity of the scanner relative to the surface of the object. Examples of position sensors, or navigators, that image two-dimensional areas of an object are disclosed in U.S. Pat. No. 5,644,139 of Allen, et al., for "Navigation Technique for Detecting Movement of Navigation Sensors Relative to an Object," and U.S. Pat. No. 5,578,813 of Allen, et al., for "Freehand Image Scanning Device Which Compensates for Non-linear Movement," both of which are hereby incorporated by reference for all that they disclose.
One portable scanner includes a contact image sensor and two navigators. The two navigators are located on one side of the contact image sensor, forming a line parallel to the contact image sensor. The two navigators are placed just close enough together so that the ends of the contact image sensor extend beyond the navigators. With this scanner configuration it can be very difficult to scan an entire object, including the edges, without rotating the scanner by at least ninety degrees. With the first scanner described the navigators will be moved off the object when the contact image sensor is moved adjacent to a top or bottom edge of the object, since the navigators are located on one side of the contact image sensor. With the second scanner described a navigator will be moved off the object when scanning the side edges of the object, since the navigators are located beyond the ends of the contact image sensor. If the navigators move off the object the position information is lost and the portable scanner may be unable to stitch the scanned strips together. Typical stitching software has a difficult time stitching scanned strips together if the portable scanner has been rotated a large amount, such as by ninety degrees. For this software, the portable scanners described above cannot fully image the edges of an object.
A need therefore exists for an image and position sensor which enable a portable scanner to fully scan an object, including the edges.